Compound master cylinder



May 16, 1950 A. Y. DODGE COIPOUND MASTER CYLINDER 3 Sheets-Sheet l Filed sept. 14. 194s A. Y. DODGE 2,507,663

couPouNn msm CYLINDER 3 Sheets-Sheet 2 May 16, 1950 Filed Sept. 14, 1945 Patented May 16, 1950 UNITED STATES PATENT OFFICE Claims.

My invention relates to hydraulic brake applying apparatus.

One of the objects of my invention is to provide improved hydraulic brake applying apparatus having at least two stages of brake ap- Diving movement, the nrst stage eilecting a relatively quick clearance take-up and the second stage effecting a relatively slow forcefulbrake applying movement, in which the transition from one stage to another will not interfere with the controllabllity of the brake or greatly aect the feel or change in resistance oi' the brake pedal.

A further object is to provide means to compensate for suddenly applied pressure Von the brake pedal in the differential type master cylinder. A sudden application o! pressure has a tendency to open the did'erentlal valve controlling communication between opposite sides oi the piston prematurely.

A further object is to secure the proper proportion between the iluid pressure opening area of the diilerential valve and the iiuid pressure closing area so that the most sudden break in the pedal pressure versus deceleration" curve will occur at low rates of decleration.

A further object is to provide an improved hydraulic brake applying apparatus which will hinder the sudden application of pressure on the brake pedal from eil'ecting a transition from rapid clearance take-up movement to slow powerful brake applying movement at too early a stage.

A further object of my invention is to provide an improved hydraulic brake applying apparatus in which the soft piston packing does not cross any port or interruption in the smooth cylinder wall.

A further object is to provide an improved dii'- ierential piston, differential valve type of pedal actuated master cylinder for brakes in which. during a ilrst stage oi' diilerential piston action, the differential valve. after opening, will close when a denite ratio between the pressure in the front and rear of the piston has been established and in which, during a later stage of differential piston action, the diilerential valve will remain open to maintain the pressure equal on both faces of the piston and in which, during the first stage as well as during the second, the pedal pressure required increases as the braking eiIect increases.

Further objects and advantages of the invention will be apparent from the description and claims.

In the drawings. in which my invention is illustrated.

Figure l is a diagrammatic view showing my brake applying apparatus in conjunction with the hydraulic brake actuators;

Fig. 2 is an axial sectional view ot the master cylinder on the line 2 2 of Fis. 3;

Fig. 3 is a transverse sectional view on the line I-I of Fig. 2:

Fig. 4 is a transverse sectional view on the line 4-4 oi Fig. 2;

Fig. 5 is a longitudinal sectional view on the line 6 5 of Fig. 3;

Fig. 6 is an enlarged sectional view showing the difierential valve; and

Fig. '1 is a chart with curves showing the relative values for certain variables.

Referring to the drawings in detail. the construction shown comprises a pedal i, shown diagrammatically in Fig. l, plvotally mounted at I, a master piston 3, the piston rod 3 of which is pivotally connected with the pedal by means of a link I, a master cylinder 5 in which the piston operates, and four hydraulic brake actuators 6, one for each of the four wheels of the vehicle for applying the brakes l when pressure is applied to the pedal at 8.

The brake applying apparatus is designed t0 provide three stages oi brake actuation-fil) a low pressure, high speed brake actuating movement for taking up the slack between the brake and the brake drum 9; (2) a high pressure, low speed movement for creating pressure between the brake and brake drum, and (3) a low pressure, high speed final brake applying movement to provide a safety feature in the event that excess wear oi' brakes or the loss of uld has occurred and because thereof the previous movement has not caused sufilcient braking pressure.

The transition from high speed. low pressure clearance take-up to low speed, high pressure braking movement is eilected by means of a spring pressed diierential valve I located in a passageway it affording communication between the cylinder chamber il in front of the piston and the cylinder chamber I2 behind the piston. When the pressure in the chamber ii in front of the piston 3 becomes suillcient to open this valve 8* against the closing pressure of the spring i2, it opens communication between opposite sides oi the piston 3, allowing uid to ow from the front chamber Ii to the rear chamber i2. When the two chambers are thus in communication, the resisting hydraulic i'orce acting on the i'ront face of the `piston is opposed by the hydraulic pressure on the rear face oi' the dlierential piston which is added to the manual pressure exerted on the piston rod by the pedal.

In order to provide a stage of braking movement in which the full force increasing ratio oi' the differential piston is made available, it is necessary that ai'ter a certain stage oi iluid pressure has been reached the diilerential valve will remain open as the pedal pressure is increased. In order to provide some correspondence between the pedal pressure required and deceleration produced during the second stage of braking action, thus avoiding a completeLv uncontrollable system, it is necessary that the amount of pedal pressure required shall increase with the amount of deceleration desired.

To accomplish this, I design the valve t* so that the fluid pressure opening area oi' the valve is greater than the iluid pressure closing area. and provide the spring I2 to assist in the closing abonnes movement, these relative areas and spring force being determined from certain equations as pointed out later. I achieve this relatively smaller iluid pressure closing area by providing the valve with a stem Il which is slidable in the bushing i8 threaded into the cylinder casing. With this construction, the tluid pressure opening area is the area of the circle at the line oi closure at i6* between the valve and its seat. and the fluid pressure closing area is equal to the area of this circle minus the cross-sectional area of the valve stem l5.

With this design. when the pressure on the pedal I at 8 and the resistance to movement of the brakes cause the iiuid pressure in front of the master piston 3 to reach a certain value. the valve opening pressure on the valve t* will overcome the valve closing action of the spring I! and the valve will open, creating a valve closing iiuid pressure on the valve. Thereafter, for any denite amount of increased pressure on the pedalI there will be a definite deter-minable pressure ratio between the fluid pressure valve opening force and the fluid pressure valve closing force, at which the valve will again seat itself, up to a certain stage oi pedal pressure. After this certain stage of pressure has been reached. an increase in pedal pressure will increase the hydraulic forces acting but will not result in a closing of the valve.

As explained mathematically hereinafter, the valve will begin its opening and closing action when the iiuid pressure on the valve is sumcient to overcome the valve closing effect oi the spring. but the valve will not remain constantly open until the pressure per square inch in front of the piston is equal to the pressure per square inch on the rear of the piston.

In order to make available a ilnal low pressure large movement of the brake applying aetuators 6 in case suillcient braking pressure has not been applied prior to the ilnal movement of the pedal l due to excessive free movement of the piston 3, I position the portion of the passageway it leading from the cylinder chamber Il so that the piston 3, toward the end of its movement. will close this portion of the passageway and prevent any further flow of liquid from the chamber il to the chamber l2. Further movement of the piston will necessarily force all of the liquid displaced from the chamber Il into the brake actuators, causing relatively high 4 speed, low pressure movement of these actuators to insure further application oi brake pressure. In general. I have found that a complete pedal movement oi' six inches gives satisfactory results 5 in eecting all three stages of pedal movement. the maximum pedal movement for the ilrst stage occurring with worn lining being about 2% inches; the pedal movement for the second stage being about three inches, and the pedal movelo ment for the third stage being about V4 inch. I have found that a tangential or circumferential movement of the ends of the brake band with respect to each other of about .45 inch will suilice to take up the greater clearance or slack between the brake band and brake drum occurring during the last stages of brake lining life and that a ilnal tangential or circumferential movement oi' the brake band ends oi about .125 inch will sufiice to enable any rate of deceleration from xero to 30 ft./sec.. I have found that the following give satisfactory results:

A mechanical advantage of 24:1 between the pedal movement and the high pressure tangential or circumferential brake applying movement;

A diameter oi one Ainch i'orthe brake applying actuator pistons 8*. and

A ratio of pedal movement to master pinion movement of 3.375 l.

Assuming the above values, it can be determined mathematically that in order for ait/4- inch movement of the brake pedal to cause a .e5-inch movement of the brake band ends, the diameter of the master cylinder piston should be 1.64 inches and its area 2.125 square inches, and that in order for three inches of pedal movement to eiiect the slow speed, high pressure movement of the brake actuators to cause a circumferential movement of the brake band ends relative to each other or l@ inch, the diameter of the piston rod should be .'15 inch and its cross-sectional area .4418 square inch.

The net hydraulic force acting on the rear face of the piston (which may be termed the diii'erential piston) is the pressure in pounds per square inch times the difference in area of the piston face and the cross-sectional area of the piston rod, or 1.683 square inches.

The comparative performances oi the brake cylinder disclosed in this application with certain other types is shown in the drawings and in the chart (Fig. 'D and in the following perfomance table used in preparing the chart.

n #2 is #4 #a Ia rr n n no m su Force oi Gross Nominal man Ne: run or nmra roion uns rms nya rom f;-

Hyd. rom #aug Nec Pedal om. Ft. on Brake Relieving Brake P. s. i. on s on Dill. um Force, Spring Pedal ses.: Ends, Lbs. s Lb slings, Pinon mlivn" rima Pm Rod Lb. rg?, n n n #sx rlx #1o-Hu spring ghn; W-m i 2.125 mm 3) Wu" spring n.5 c 4o 4o s1 was o o maa n 4 :lo s es 4o 12 v2. a :n.1 .i .i mi as e g' s 'n 1o so 1s sr.: 11 442 4o m as taza s 1,0m 21s sin an u m :ou as m ai 14e SIGNAL AND SAFETY rmrUns-rIsroN nur SAFETY roar i iu :n1 1s 1 su m ins Large piston area-2.126. Small piston aree-Mis. Valve bead-.lu sq. in. Valve stam-.Nl lq. in.

Itwillbeshownthatforanydeilnite cnthepedaitherewillbeacorrespondingforce tending to separate the ends of the brake hands and consequently a corresponding deceleration in feet per second squared, or vice versa, that for any definite deceleration in feet per second squared there will be a corresponding pedal pressure required.

In arriving at the formulas or equations i'cr computing the pedal pressure required for a given deceleration. certain variables in the performance table must be taken into account, as follows:

Column No. 1,-The deceleration in ftfsec;

Column No. 2.-The net force on the brake ends in pounds;

Column No. 3.-'I'he force in pounds of the brake relieving springs il;

Column No. The gross force on the brake actuator pistons;

Column No. 5.The pressure in #/sq. in. in front of the master piston and in the brake actuating cylinders;

Column No. 6.-The force due to premure in front of the master piston;

Column No. 7.-'1'he pressure per square inch on the rear side of the master piston (auxiliary cylinder) Column No. 8.-The force in pounds on the di'erential piston;

Column No. 9.-The manual force exerted on the piston rod;

Column No. 10.-'Ihe net force exerted on the Column No. 11.-The force in pounds exerted by the pedal returning spring i3; and

Column No.- 12.-The gross force in pounds exerted on the pedal.

Before making the computations necessary in filling out this tabie, it is necessary to ilnd the value of the pressure behind the master piston in terms of the pressure in front of the master piston, as determined by the ratio of the iiuid pressure opening area of the valve to the iluid pressure closing area and to the strength oi' the spring I2. I have found that with the assumed one-inch diameter brake applying pistons and the 1.64-inch diameter of the master cylinder piston, a. iiuid pressure opening area of the valve l* of .162 sq. in. and a uid pressure closing area of .138 sq. in., with a valve spring force of 15 pounds. give satisfactory results. Designating the pressure in front of the master piston'as Pi, liquid pressure on the back of the piston as Pz, the fluid pressure valve opening area as ai, the iluid pressure valve closing area as az, and the spring pressure as Fs, we have the equation: Pzxa2=P1xai-Fs. Substituting values for a1, o: and Fs, we have the equation Pq=P1 X 1.173- 108.5

Referring now to the perfomance table, assume that it is desired to iind the gross pedal pressure required to effect the various decelerations expressed in the first column of the table. The values expressed in columns 3 and l1 are arbitrary. depending upon the kind of springs used. However, the values of the spring forces indicated have been found satisfactory.

In general, it may be assumed that the values in column 2 in pounds force on brake band ends are twenty-six times the values in column 1 in deceleration in feet per second squared. As indicated above, in column 3, the values for the pound force of the brake returning spring are arbitrary. The gross force on the brake pistons 0 (colimn 4) is obvlciy the sum of the correspondilmguresoi'columnsZands. Theline messmepersquareinchinfrontofthemaster piston (column 5) is obviously the value e incolumn4,dividedbytheareaofthebrake actuator piston lI (.784 sq. inJ. The hydraulic force acting on the front oi.' the master piston (column B) is the product of the line pressure in collnnntimestheareaofthemasterpiston (2.125 sq. in). The pressure per square inch in the auxiliary cylinder is calculated from this equation P:=(P1x1.1'l3) 108.5, using the designated value for P1 in column 6. The hydraulic force in pounds on the differential piston (column 8) is the value for P: as given in column 7, times the difference in area between the master piston face and the cross-sectional area of the piston rod, which diilerence equals 1.683 square inches. The manual force required on the master piston rod (column 9) is the diilerence between the hydraulic force acting on the large piston, expressed in column 6, and the hydraulic force on the dii ferentiai piston expressed in column il. The net pedal force in pounds (column 10) is the manual force on the master piston rod as expressed in column 9, divided by the ratio of movement o! the pedal with respect to the master piston movement (3.375). The values indicated in column 1l for the force of the pedal returning spring are empirical as indicated above. The nominal gross pedal pressure expressed in column 12 is obviously the sum of the net pedal pressure expressed in column l0, plus the empirical spring premure value in column 11. Using the above equations and formulas, it is found that the gross pedal forces required for the indicated deceleration values in column l are as indicated in column 12.

Fig. 'l' shows certain curves plotted against pedal movement in inches. Pedal movement in inches is divided into three sections, (l) a slack take-up movement of 0:25. inch; (2) a brake applying movement oi' 3 inches. and (3) an emergency safety movement of three-fourths o! an inch.

In this chart, the curve B, plotted against the pedal pressure scale #l and the corresponding deceleration curve F. plotted against the deceleration scale #2, indicate perfomance of the apparatus described in this application, in which A1=2.12, A3=1.68, 111:.162 and az=1.38, from which it follows that In all three curves a spring assumed.

These curves are plotted trom values which can be obtained by calculation, using the above equations, after ilrst obtaining the values in the preceding perfomance table.

In order to provide some correspondence beiorce Fs=l5 lbs. is

mf am; E ma.. z Emmm m L: www Hh @m www my# .mm m mm?. ffii? if mg mmmmmmmmmm m .mm.m @mm m mmmmm i W ,WWE m ..m ,mm mm W. W m mmm ...mfmmwnrk www mmmmmm n #n iA/m A13... mmmmmm mi m .mmm W. W Mm l mmmmmmmmmm mmmmmmmmhmmmm bjww A jm u m nu .df n u u u mm mfmmmmmm@ m mmm mm which nts into a cylindrical portion of the valve casing when the valve is closed so that there is very little port opening until the cylindrical portion of the valve Is completely out oi the cylindrical recess in the casing. As a iurther precaution. I provide a dash pot construction to control the opening movement of the valve. For this purpose the valve stand I! extends into a dash pot chamber Il from which restricted openings I! and 2l lead to the low pressure side oi' the system. As a further precaution, I provide labyrinthlne passage restriction in the passage Ill shown in Fig. 5. This labyrinthine construction may be provided by slipping into the passage II) small cylinders 2 I, each having a restricted opening 22, these cylinders alternating with cylindrical shells 23 so that each restriction is iollowed by a rather large chamber into which the iet of liquid discharges resulting in turbulence and retarded iiow.

When the pedal pressure is released, the springs Il draw the ends of the brake bands I together forcing liquid back from the cylinders 8 into the master cylinder I in front of the piston 8. The pressure of this liquid plus the pedal returning action of the spring I3 moves the piston 3 toward withdrawing position. Any deilciency in liquid supplied to the chamber II of the master cylinder 5 from the brake actuating cylinder 6 is made up by liquid supplied from the low pressure side of the piston through the port 24 and passage 25, past the check valve 28 to the chamber I I in iront of the piston 3. When the piston is in fully withdrawn position. the iront edge of the piston uncovers the port 2I to permit the supply oi liquid to the cylinder chamber II directly from the reservoir.

It is sometimes desirable that a light iluid pressure be applied to the liquid in the reservoir. For this purpose I provide a connection from the exhaust manifold opening into the reservoir above the liquid level therein. Referring to Fig. 2, the construction shown for this purpose comprises a tube 28 connected with the exhaust manifold, a trap 28 into whch this tube leads for separating foreign material, and a check valve 80 for preventing return flow of the gas delivered from the exhaust manifold. In order to prevent excessive pressure in the liquid reservoir, I provide a relief or safety valve II which may be set so as to release pressure at a relatively low amount, perhaps three or four pounds pressure.

Flow from the reservoir 32 to the rear chamber I2 is through the passage 33 (Figs. l and 4) past the check valve 34, and through the passage 35.

It will be seen that there are two ports 21 and 35 opening into the front and rear cylinders II and I2,`respectively, from the reservoir 32, both of which are alternately opened and closed by movement o1' the piston 3 and that there are two check valve-controlled ported passages III and 25 opening into both the front chamber I I and the rear chamber I2. the passage IB connecting the front and rear chambers for flow from front to rear, and the passage 25 connecting the front and rear chambers for flow from rear to front, the

ports for these passages also being alternately nect cylinder portion II with cylinder .portion I2 on increase oi iluid pressure due to pedal application. The check valve 2l and passages 2l and 2l let the cylinder portion Il till from the cylinder portion I2 on pedal release. The check valve and passages 22 and 3l enable ow from reservoir 22 to cylinder portion I2 on pedal application until check valve 9 opens to supply cylinder portion Il from cylinder portion I2. The port 21 enables now from reservoir I2 to cylinder portion II when the pedal is released.

Referring again to the chart Fig. '1, the point X on the curves B, C and D at which differential action o: the cylinder begins is obtained as iollows. As P1 increases, it reaches a value at which the iluid opening pressure on the valve 9* will overcome the valve closing e'ect of the spring I2. At this point P1a1=Fs. Substituting values .182 Pi==15 or Pi=92.6 lbs/sq. in. Referring to the table, this value of P1 corresponds to a pedal pressure of 64 lbs. and a deceleration of 1 it./sec..

Further modiilcations will be apparent to those skilled in the art and it is desired. therefore, that the invention be limited only by the scope of the appended claims.

Having thus described my invention, what I claim and desire to secure by Letters Patent is:

1. A master cylinder having a differential piston and having means ailording communication between the iront face and the rear face oi the piston, a differential valve controlling said communication and spring means tending to close said valve, the dlierential valve having a valve opening area exposed to the pressure created in the cylinder in front of the piston and a valveclosing area exposed to the pressure created in the cylinder in the rear of the piston the pressure eil'ective front face o1 the piston being greater than the pressure effective rear face of the piston, the pressure opening valve area being greater than the pressure closing valve area, and the quotient of the iront piston face area divided by the rear piston face area being greater than the quotient of the pressure opening area divided by the pressure closing valve area.

2. A master cylinder and piston construction comprising a cylinder, a piston rod and a piston secured to said rod, said cylinder having a port through which iluid is forced to a pressure-actuated actuator to which a varying resistance is opposed, said construction having a passage between the chamber on the piston rod side oi' the piston to the chamber on the other side of the piston, a valve port in said passage and a spring closed valve for said port in said passage opened by the rise in pressure in the chamber on said other side of said piston, said valve having a cylindrical portion fitting into a cylindrical recess of the valve port when closed and movable out oi said recess when open whereby slight initial movement of the valve due to short iluctuations of pressure will not cause the cylindrical part oi' the valve to move out oi' the cylindrical portion of the valve port.

3. A master cylinder and piston construction comprising a cylinder, a piston rod and a piston secured to said rod, said cylinder having a port through which fluid is forced to a pressure-actuated actuator to which a varying resistance is opposed, said construction having a passage between the chamber on the piston rod side of the piston to the chamber on the other side of the piston, a spring closed valve in said passage opened by the rise in pressure in the chamber on said other side of said piston, and a dash pot for asomo:

11 controlling said valve to prevent sudden application of force Iro'rn opening the valve prematurely comprising a plunger actuated by said valve and a restricted orince through which iiuid is forced by said plunger.

4. A master cylinder and piston construction comprising a cylinder, a piston rod and a piston secured to said rod, said cylinder having a port through which duid is forced to a pressure-actuated actuator to which a varying resistance is opposed, said construction having a labyrinthine passage between the chamber on the piston rod side ci the piston to the chamber on the other side of the piston, and a spring closed valve in said passage opened by the rise in pressure in the chamber on said other side of said piston to prevent sudden application o! force from opening the valve prematurely.

5. A master cylinder having a differential pislton and having means aifording communication between the front face and the rear face of the piston. a differential valve controlling said communication and spring means tending to close said valve, the differential valve having a valve opening'area exposed to the pressure created in the cylinder ln iront of the piston and a vaiveclosing area exposed to the pressure created in the cylinder in the rear of the piston the pressure elective front race o1 the piston being greater than the pressure eilective rear tace of the piston, the pressure opening valve area being greater than the pressure closing valve area, and the l2 quotient of the iront piston tace area divided by the rear piston face area being sreater than the quotient ot the pressure opening valve area divided by the pressure closing valve area. the range of movement o! said piston being such that at some point in its range the pressure per unit area on theiront tace oi' the piston is equal to the spring valve closing force divided by the dliierence in area of the valve orpening` area and the valve closing area.

ADEL Y. DODGE.

REFERENCES CITED The following references are of record in the file o! this patent:

UNITED STATES Pam'rs Number Name Date 1,084,715 Steinmann Jan. zo, 1914 1,111,556 Bakels Sept. 22, 1914 1,695,194 Lansinger Dec. 11, 1928 1,919,482 Penta Aug. 18, 1931 2,180,454 Bowen Nov. 31, 1939 2,184,501 Loweke Dec. 26, 1939 2,185,072 Bowen Dec. 26, 1939 2,328,603 Schnell Sept. 7, 1943 2,340,113 Dodge Jan. 25, 1944 FOREIGN PATENTS Number Country Date 607,748 Germany Jan. 12, 1935 

